(Field of the Invention)
The present invention relates to a cooling structure for a bearing device, and relates to, for example, a cooling structure for a bearing device in a spindle device of a machine tool.
(Description of Related Art)
For spindle devices of machine tools, the temperature increase in the devices needs to be kept small in order to ensure the processing accuracy. However, the speed for, the recent machine tools tends to increase in order to, improve the processing efficiency, and the amount of heat generated from the bearing that supports the spindle also tends to increase, along with this increase in speed. The so-called motor built-in spindle devices including a driving motor incorporated therein are increasing in number, which also cause heat generation.
Heat generation during the rotation of the bearing leads to an increase in the pressure on the surface of contact between bearing rings and rolling elements, resulting, in an increased risk of damage to the bearing. Accordingly, in view of a higher speed and a higher precision of the spindle, the temperature increase in the bearing caused by heat generation needs to be minimized. As means for suppressing the temperature increase in the bearing, a method is available in which cooling is performed by injecting a cooling fluid formed of a mixture of an air and an oil, or formed of only an air to the bearing during operation.
By enhancing the bearing cooling effect by injecting the cooling fluid to the bearing during operation, the operation can be performed at a higher speed. However, an air curtain formed of a swirl flow about the axis is generated in the vicinity of revolving rolling elements, and injecting a large amount of the cooling fluid toward this air curtain results in the generation of sound of collision, which is collision noise. Therefore, it has been attempted to reduce noise by inclining the orientation of a nozzle configured to inject the cooling fluid, forwardly in the rotation direction of the spindle (e.g., Patent Documents 1 to 4).